The spotted jelly (Mastigias papua), lagoon jelly, golden medusa, or Papuan jellyfish, is a species of jellyfish from the Indo-Pacific oceans. Like corals, sea anemones, and other sea jellies, it belongs to the phylum Cnidaria. Mastigias papua is one of the numerous marine animals living in symbiosis with zooxanthellae, a photosynthetic alga.[1]
Five subspecies have been described, inhabiting separate marine lakes in the Palau group.[2]
The spotted jelly has distinctive spots atop its bell, and vary in colouration, from greenish blue to olive green, which can be attributed to the zooxanthellae which reside within their tissues. [3]
They have 8 frilled oral arms, which end in a clublike appendage. The upper surfaces of these arms are covered in stinging cells called cnidocytes. [4] Unlike many other jellies, spotted jellyfish have numerous mouths along the bottom of their oral arms.
There are eight rhopalia, which act as the sensory organs of the jellyfish, on the margin of the bell.
They average 10cm (4 in) in diameter, but can grow as large as 30 cm (12 in).
These jellies feed on zooplankton and other tiny organisms using their stinging cells, called cnidocytes. The spotted jelly has several small mouths used to grab animal plankton.
Spotted jellies also acquire much of their nutrition via an endosymbiotic relationship with photosynthetic zooxathellae, such as those of the genus Cladocopium. [5] The zooxathellae provide the jellyfish with nutrients, and in return the zooxanthellae get a safe place to live. This symbiotic relationship is not unique to the spotted jellyfish, and can also be observed in species such as the upside-down jellyfish.
During the night, these jellyfish stay lower in the water column and migrate each day, rising to the waters surface, and following the sun east to west, to allow their zooxanthellae access to the light they need to photosynthesize. [6] [7]
Spotted jellies range throughout the Indo-Pacific, from the Fijian Islands to the western Indian Ocean, and from Japan to Australia.[8]
Some populations of spotted jellies in Palau have been found to occur in huge groups (called "smacks"), which have become tourist attractions. The most famous spot to admire them is the Ongeim’l Tketau Lake in Palau, also known as Jellyfish Lake. [9]
Spotted jellies are predated upon by the sea anemone Entacmaea medusivora, which capture the jellyfish in their tentacles. While the jellyfish is captured by the anemone, an enterprising gastropod or fish may scavenge upon the captured jellyfish before the anemone is finished consuming it. [10]